[tools][fix] 修改 iar.py 中 iar 版本查找失败后的处理，目的是在出错后终止 scons 程序，以发现并修改错误；并在成功后打印 iar 版本，便于调试

Signed-off-by: MurphyZhao <d2014zjt@163.com>

tools/iar.py

@@ -194,10 +194,12 @@ def IARVersion():
         cmd = os.path.join(path, 'iccarm.exe')
     else:
         print('Error: get IAR version failed. Please update the IAR installation path in rtconfig.py!')
-        return "0.0"
+        exit(-1)
 
     child = subprocess.Popen([cmd, '--version'], stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True)
     stdout, stderr = child.communicate()
 
     # example stdout: IAR ANSI C/C++ Compiler V8.20.1.14183/W32 for ARM
-    return re.search('[\d\.]+', stdout).group(0)
+    iar_version = re.search('[\d\.]+', stdout).group(0)
+    print("IAR version: %s" % iar_version)
+    return iar_version